While on the big island for almost 2 weeks in 2k3, we never stayed in a hotel. We camped. There are a ton of county parks which are right on the shore in various spots and we stayed at a different one almost every night. It was beautiful to cook/have our meals right at our ocean front 'room'. We stayed in a B&B the last couple of nights. We did stay in the campground at Volcano NP a couple of nights also. That was different and special in its own way. All this was easy on the budget, and completely avoided the resort scene, which my family dislikes.
Diving on the big island was really good.
We went to Kauii as part of the trip and spent a week there, staying at a working farm in a guesthouse. I dove at Niihau and that was among the really special experiences I have had diving.
We had avoided Hawaii in general because we are not really 'resort' people. But once we found the alternatives, it turned out to be a really great trip.